This invention pertains to fasteners. More particularly, the invention pertains to a nail with a shank having a plurality of grooves configured to reduce the amount of material needed to create the nail and increase the holding power of the nail, while only minimally affecting the bending yield strength of the nail and other important properties of the nail.
Round nails (nails having cylindrical shanks) have been produced for hundreds of years. Not only are round nails the easiest type of nail to manufacture, because of their symmetrical shape round nails exhibit predictable, uniform properties in any direction when driven into wood, their largest application. Such properties include holding power and bending yield strength.
Holding power, or withdrawal strength, refers to the nail's resistance to an axial force (a load parallel to the nail shank). Holding power includes not only the nail's resistance to withdrawing from the substrate into which it is driven, but also to the nail's resistance to “pull through.” Pull through occurs when the head of the nail is pulled through the structural element being attached to the substrate. Bending yield strength refers to the nail's resistance to bending (a load perpendicular to the nail shank).
Most round nails are manufactured from steel. It has been estimated that more than 70-80% of the total cost to manufacture a nail comes from the raw material used to make the nail. As the cost of steel and other raw materials used to manufacture nails continues to rise, it would be desirable to minimize the manufacturing cost by creating a nail that uses less material without significantly adversely affecting the desirable physical properties of the nail, such as holding power and bending yield strength. Additionally, it would be desirable that such reduction in material does not affect the head geometry of the nail, such that a full round head may be used in order to maintain a sufficiently high pull through resistance.
The prior art has altered the shape of the nail shank in order to increase holding power. For example, U.S. Pat. No. 5,143,501 for a “Grooved Nail and Strip” by Leistner et al. discloses a nail having a shank formed with grooves formed along the shank. The shape and number of the grooves vary over several disclosed embodiments. Similarly, U.S. Pat. Nos. 4,755,091 and 4,815,910 by Potucek for a “Star Fastener” and a “Collated Nail Strip,” respectively, disclose a nail with a star-shaped shank.
As discussed above, a nail with a full round head is desirable in order to provide increased pull through resistance. Moreover, a nail with an enlarged full round head provides even greater pull through resistance. Examples of such nails having enlarged round heads are disclosed in U.S. Pat. No. 5,741,104 by Lat et al. for a “Steel Fastener Having Grooved Shank” and U.S. Pat. No. 6,758,018 by Sutt, Jr. for “Power Driven Nails for Sheathing Having Enlarged Diameter Heads for Enhanced Retention and Method.”
While the disclosed prior art shank designs seek to increase the holding power of the nail, such prior art nails do not have the same bending yield strength and other important properties in all directions as non-grooved nails. Moreover, because the prior art designs use a relatively small number of relatively large grooves that extend deeply into the shank, the shape and size of the head of such prior art nails may be limited. However, if the grooves formed in the shank extend too far into the body of the shank, the resulting shank geometry does not permit the nail to have a full round head, or a head of sufficient size to provide a desirably pull through resistance.
Accordingly, there exists a need for a nail configured to reduce the amount of material needed to create the nail while at the same time increasing holding power and only minimally affecting the bending yield strength of the nail. Desirably, such a nail includes a relatively large number of relatively shallow grooves disposed about the circumference of the shank. More desirably, formation of the grooves does not alter the geometry of the shank such that the nail cannot have a full round head. More desirably still, the grooves may be formed with deformations to increase the holding power of the nail. Most desirably, the grooves may be combined with protrusions extending outwardly from the shank in order to increase the moment of inertia of the nail, and to further increase the holding power and bending yield strength of the nail.